Electronic device and actuator using the same

Abstract

An electronic device has a substrate, a heat sink, and a heat conductive material. The substrate has a first surface on which an electronic part is arranged. The heat sink has (i) a second surface facing the first surface and distanced from the electronic part and (ii) an annular groove extending annularly and defining an area that is circled by the annular groove on the second surface and faces the electronic part. The heat conductive material is arranged between the first surface and the second surface to be in contact with the electronic part and the annular groove. The heat conductive material guides heat generated by the electronic part to the heat sink.

What is claimed is: 
     
       1. An electronic device comprising:
 a substrate having a first surface on which a plurality of electronic parts are arranged;
 a heat sink that has a second surface facing the first surface and distanced from the plurality of electronic parts, each of the electronic parts associated with: 
 
 (i) an outer annular groove extending annularly in the second surface and defining an outer area that is circled by the outer annular groove on the second surface, the outer area facing a corresponding one of the electronic parts, the outer annular groove is only outside of a footprint of the corresponding one of the electronic parts; 
 (ii) an inner annular groove extending annularly in the second surface and defining an inner area that is circled by the inner annular groove on the second surface, the inner area facing the corresponding one of the electronic parts, the inner annular groove is only inside the footprint of the corresponding one of the electronic parts; 
 (iii) a heat conductive material that is arranged between the first surface and the second surface to be in contact with the corresponding one of the electronic parts, the outer annular groove, and the inner annular groove, the heat conductive material guiding heat generated by the corresponding one of the electronic parts to the heat sink; and 
 (iv) an application area on the second surface, configured for application of the heat conductive material, the application area encompassing the outer area, and a projected view of the application area overlaps the inner annular groove and the outer annular groove. 
 
     
     
       2. The electronic device according to  claim 1 , wherein the outer annular groove extends to have a ring shape and the inner annular groove extends to have a ring shape. 
     
     
       3. The electronic device according to  claim 1 , wherein the outer annular groove or the inner annular groove has a sidewall surface that inclines with respect to a direction perpendicular to the second surface. 
     
     
       4. The electronic device according to  claim 3 , wherein
 the sidewall surface includes a bottom end and an opening end that are opposite to each other in the direction perpendicular to the second surface, and
 the bottom end is located on a radial outer side of the opening end in a radial direction of the outer annular groove or the inner annular groove. 
 
 
     
     
       5. An actuator comprising:
 the electronic device according to  claim 1 ; and 
 a rotational electric machine of which energization is controlled by the electronic device, the rotation electric machine operating a load rotatably.